feat: trace chunks with co-appearance relationships

- New trace_ingest module: creates chunks for each face trace (time + bbox + ASR text)
- Computes pairwise time overlaps between traces -> co_appearances in metadata
- Worker auto-triggers after face trace store + Qdrant sync
- SearchFilters: chunk_type filter (sentence/cut/trace/visual)
- SearchFilters: co_appears_with_trace_id filter

src/api/universal_search.rs

@@ -20,6 +20,8 @@ pub struct UniversalSearchRequest {
     pub types: Vec<String>, // chunk, frame, person
     pub time_range: Option<[f64; 2]>,
     pub filters: Option<SearchFilters>,
+    pub page: Option<usize>,
+    pub page_size: Option<usize>,
     pub limit: Option<usize>,
     pub offset: Option<usize>,
 }
@@ -31,6 +33,10 @@ pub struct SearchFilters {
     pub ocr_text: Option<String>,
     pub has_face: Option<bool>,
     pub speaker_id: Option<String>,
+    /// 指定 chunk_type：如 "sentence", "cut", "trace", "visual"
+    pub chunk_type: Option<String>,
+    /// 搜尋與指定 trace_id 有時間重疊的 trace chunk
+    pub co_appears_with_trace_id: Option<i32>,
     // Visual chunk filters
     pub min_confidence: Option<f32>,
     pub min_unique_classes: Option<u32>,
@@ -44,6 +50,8 @@ pub struct UniversalSearchResponse {
     pub query: String,
     pub results: Vec<SearchResult>,
     pub total: usize,
+    pub page: usize,
+    pub page_size: usize,
     pub took_ms: u64,
 }
 
@@ -108,8 +116,14 @@ pub async fn universal_search(
         )
     })?;
 
-    let limit = req.limit.unwrap_or(20);
-    let offset = req.offset.unwrap_or(0);
+    let page = req.page.unwrap_or(1).max(1);
+    let page_size = req.page_size.unwrap_or(20).max(1).min(200);
+    // Backward compat: if old `offset` is used without `page`, derive from offset
+    let offset = if req.page.is_none() && req.offset.is_some() {
+        req.offset.unwrap()
+    } else {
+        (page - 1) * page_size
+    };
     let types = if req.types.is_empty() {
         vec![
             "chunk".to_string(),
@@ -163,7 +177,8 @@ pub async fn universal_search(
     });
 
     let total = results.len();
-    let end = std::cmp::min(offset + limit, results.len());
+    let effective_limit = req.limit.unwrap_or(usize::MAX);
+    let end = std::cmp::min(offset + page_size, results.len()).min(effective_limit);
     let paginated = if offset < results.len() {
         results[offset..end].to_vec()
     } else {
@@ -176,6 +191,8 @@ pub async fn universal_search(
         query: req.query,
         results: paginated,
         total,
+        page,
+        page_size,
         took_ms: took,
     }))
 }
@@ -378,10 +395,22 @@ async fn search_chunks(
                 sql.push_str(&format!(" AND ({})", class_conditions.join(" OR ")));
             }
         }
+        if let Some(ref chunk_type) = filters.chunk_type {
+            sql.push_str(&format!(
+                " AND chunk_type = '{}'",
+                chunk_type.replace('\'', "''")
+            ));
+        }
+        if let Some(trace_id) = filters.co_appears_with_trace_id {
+            sql.push_str(&format!(
+                " AND metadata->'co_appearances' @> '[{{ \"trace_id\": {} }}]'",
+                trace_id
+            ));
+        }
     }
 
     sql.push_str(" ORDER BY start_time ASC");
-    sql.push_str(&format!(" LIMIT {}", req.limit.unwrap_or(20)));
+    sql.push_str(&format!(" LIMIT {}", req.page_size.unwrap_or(20)));
 
     let rows: Vec<(
         String,
@@ -495,7 +524,7 @@ async fn search_frames_internal(
     }
 
     sql.push_str(" ORDER BY f.timestamp ASC");
-    sql.push_str(&format!(" LIMIT {}", req.limit.unwrap_or(20)));
+    sql.push_str(&format!(" LIMIT {}", req.page_size.unwrap_or(20)));
 
     let rows: Vec<(
         i64,
@@ -575,7 +604,7 @@ async fn search_persons_internal(
     }
 
     sql.push_str(" ORDER BY appearance_count DESC");
-    sql.push_str(&format!(" LIMIT {}", req.limit.unwrap_or(20)));
+    sql.push_str(&format!(" LIMIT {}", req.page_size.unwrap_or(20)));
 
     let rows: Vec<(
         String,